I have had some confusing experiences with dial up modems.
My first PC (Pentium75) was treated to a new 56K V92 external modem
and the computer store had all sorts of fun trying to get this modem
working at all. Eventually they discarded the supplied driver CD and
found a driver off the net that got it working, albeit slowly but at
the time I didn't know what a fast connection was........
My next PC (Celeron 500) somebody said get an internal modem so I
bought a Netcomm IN5699_4 56KV92 and with the supplied drivers it was
a rocketship on rails compared to my previous external modem.
A friend bought his first PC (P4 1.8) and because I had such a good
experience with my Netcomm I suggested he get that brand. He bought a
Netcomm IN5920_1 internal modem which didn't work well at all. After a
struggle with different drivers we learned that this modem would only
work properly with WinME or later and my friend was running Win98se.
He then bought an unbranded internal 56KV92 which worked but at a
snails pace......
I loaned him my Netcomm IN5699_4 internal and his internet speed was
then better than I was getting with my Cel500 so we then searched high
and low and found him an identical Netcomm IN5699_4 and all was well
thank god!!
Before I attempted my move to Ubuntu I did read that internal
Winmodems were a problem.Only external hardware modems were recommended for dialup so
thats what I have now on my new PC (P4 2.6)
My dialup speed is now WAY better than I can get using my Cel500 with
the good Netcomm IN5699_4

My question may have been
a bit misleading,
because I'm not using Linux online. I'm just trying
to get my feet wet with
Ubuntu before I try that. From answers like yours and
others, I've deduced
that I'm going to have to get an alternative to my
Winmodem before I try
online dialup with Linux. Yet another hurdle. C'est
la vie.